Green said it looked very difficult for the Coalition to avoid losing any seats in Victoria, with Corangamite and Dunkley now notionally Labor after a redistribution and the ALP also expecting to take Chisolm.

He said if Labor also picked up a seat or two in Queensland, it would be pretty clear which way the wind was blowing by the time results started coming through in WA.

"I think the key thing to say about Western Australia and Queensland is for Labor to have any significant majority, they need to gain seats in Queensland and Western Australia," he said.

"For Labor's purpose, Western Australia may not determine the result, but it may have a significant impact on the size of any Labor government's majority."

That explains why Prime Minister Scott Morrison and Opposition Leader Bill Shorten have been travelling west more often than their counterparts did during previous election campaigns.

Mr Shorten is in Perth again today for a business breakfast and more marginal seat campaigning, while Mr Morrison made a flying visit on Monday afternoon to launch the Liberals' WA campaign.

Swings and roundabouts

If the election is tight, every state and every seat becomes even more critical.

Election analyst William Bowe said a close finish was still a clear possibility and it was not out of the question that WA could decide the result — the Coalition could cling to power by holding its marginal seats in Perth or Labor could tip over the line in the west.

Mr Bowe said it would likely be a close result, because Labor was struggling more than expected in regional Queensland, and the Coalition had gone on the offensive against Labor seats in northern Tasmania and the seat of Solomon in the Northern Territory, among others.

If the Coalition did well in those seats and held on elsewhere, then WA could be critical.

Spectre of 1998 election looms

This scenario was the case in the 1998 GST election, when Labor won 50.98 per cent of the two-party preferred vote to the Coalition's 49.02 per cent but did not secure enough seats to take power.

Then prime minister John Howard had to wait until the results came in from WA to confirm he had survived a huge, but uneven, swing against him.

"This could be the first election since 1998, and 2016 to an extent, where you could have been waiting on Western Australia to really turn up a surprise that might change the situation one way or another," Mr Bowe said.

"I think there's a good chance that it will be close enough that on the night everyone will be sweating on WA to see if those seats where the Liberals are under pressure are going to stay with them or not."

"I think if WA's not looking interesting on election night, it's most likely to be because Labor has it wrapped up."